Porous metal



Patented Aug. 24, 1943 POROUS METAL Roland P. Koehring, Dayton; Ohio, asslgnor to General Motors Corporation, Detroit, Mich a corporation of Delaware No Drawing. Application April 4, 1941, Serial No. 386,918

8 Claims.

This invention relates to powdered iron and to articles formed therefrom.

An object of the invention is to provide powdered iron material which is coated with a metallic material whereby articles may be formed therefrom which have a structure of iron com- Dletely coated with a film of another metal which is substantially insoluble in the iron. Another object is to provide an iron article of high porosity wherein the iron is bonded together by means of a lower melting point metal into a strong porous article having a surface which in itself is not a ferrous metal.

In carrying out the above object, it is another object to coat the iron powder with litharge which litharge may be substantially reduced during the sintering period to form a lead coating over the entire porous surface of the article.

A further object is to provide a porous ferrous article which has a coating thereover of a substantially non-corrosive metal.

Further objects and advantages of the present invention will be apparent from the following description.

In making porous articles from iron, it is diflicult to obtain strong highly porous articles without adding additional metals to the iron such as, copper, when the iron is sintered in the loose non-compacted condition. While this invention is not specifically limited to the use of iron in the non-compacted condition, it is to be understood that the present invention normally facilitates operations on non-compacted iron powder. Further, the present invention permits lower sintering temperatures when operating on iron powder due to the fact that a low melting point bonding metal is present. Lead, Bismuth or Cadmium or metals which are substantially insoluble in iron and have low melting points may be coated on the surface of the iron in a number of manners for example, by ball-milling with the iron in substantial quantities of soft metal powder whereby the powder is distributed over the surfaces of the iron powder and attached thereto through the use of some bonding material such as lacquer, etc., in which case it is desirable to have the soft metal powder of considerably smaller grain size than the iron powder.

This invention further contemplates the use. of such an impalpable powder as lead oxide which can be easily comminuted and which when mixed with iron powder readily adheres to the surface thereof without the ,use of a binder due to the fine nature of the powder. In this case, suitable quantities of litharge for example, are added to iron powder and are ball-milled until each particle of iron is coated with a coating of litharge. The iron powder is then molded in the briquetted or loose non-compacted condition to the desired shape and sintered at temperatures considerably below the melting point of iron but above the melting point of lead in a reducing atmosphere of such a character that the litharge is reduced to metallic lead in situ upon the surface of each particle of iron to form a lead coating thereover and simultaneously bond adjacent particles of iron together into a strong porous structure. The quantity of litharge to be utilized may be calculated so that the final article contains the desired percentage of lead. Oneexample, which may be given is where 30 parts of litharge are. hall-milled with parts of iron powder of the desired size until'the litharge completely coats the iron powder. The coated powder is filled into molds of the desired configuration or spread into sheets on a non adhering surface and the powder is then sintered at temperatures ranging from a 1,000 to 2,000 degree F. and for periods ranging from 10 minutes to an hour according to the temperature utilized under suitable reducing conditions, for example, in an atmosphere bf hydrogen, hydrogen diluted with nitrogen, incompletely burned natural gas,

.etc., whereupon the. litharge is reduced to mewhich has a corrosion resistant metallic constitucut over the entire porous surface thereof thereby reducing the cost of such a filter over a bronze filter and likewise providing a desirable surface thereon. The lead or other insoluble low melting point metal may be used up to 40% by weight of the total metal powder being used, however, the specific quantities of low melting point metal powder to be used are best arrived by treatment for the specific use intended for the article to be manufactured. v

Small quantities of alloying ingredients such as nickel, molybdeum, vanadium, chromium, etc.,

56 have no deleterious effects when present in the 2 iron although for reasons of economy substantially pure iron powder is preferably used since the iron itself is not exposed at any point.

In the foregoing, it will be apparent that the method and article formed thereby as disclosed herein, propose an economical expedient producing filters of the desired surface characteristics.

So far as I am aware the method proposed herein is the only satisfactory way of coating noncompacted iron with lead in the form of a porous mass since it is difllcult to mix lead and iron powder due to their-different density to obtain a uniform distribution thereof and, in the 'noncompacted condition, upon slntering the distribution of the lead would tend to be greatest at the bottom of the article and it is doubtful as to whether the upper portion of the article would be completely coated with the lead. It is also apparent, that if small quantities of alloyed ingredients are added to the lead that this fact does not exclude satisfactory operation of the method for example, the lead powder may include small quantities of antimony, tin, cadmium, bismuth, etc., without unduly effecting the success of the process. It is to be understood, therefore, that when lead is mentioned in the appended cl'aims that the term is of sumcient scope to embrace high lead alloys containing other metals in quantities up to While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms lead but below the melting point of iron and for a time-sufficient to cause the molten lead to flow uniformly over the particles of iron, and then cooling the article so formed to solidify the lead and cause the lead to bond adjacentv particles of iron together toform a strong porous article.

3. In a method of making porous iron articles the steps comprising "coating iron powder with lead oxide powder, molding the iron powder so coated into an article of the desired shape heating the molded iron powder under reducing conditions at a. temperature and for a time suflicient to cause the oxide to become reduced to elementary lead, and simultaneously to become molten and flow uniformly .over adjacent particles of iron and then cooling the article whereby the lead solidifies and bonds adjacent particles of iron together to form a strong porous article.

4. In a method of forming porous'ferrous articles from molded iron powder that is coated with lead oxide the step comprising, sintering the molded powder in a reducing atmosphere for simultaneously reducing the oxide to lead and for melting the lead to-cause the same to flow uniformly over the particles of iron.

5. A filter element comprising a highly porous I mass of iron particles bonded together by means might be adopted, all coming within the scope of the claims which follow. What is claimed'is as follows:

1. In a method of making articles from porous iron the steps comprising, coating iron particles with a material taken from the class consisting of lead and litharge, molding the iron powder to the desired shape in the loose non-compacted condition and then sintering the coated article at a temperature above the melting point of lead and below the melting point of iron for a time suihcient to cause the lead' to become molten and flow uniformly over the particles of iron, said sintering beingcarried out under suitable reducing conditions, and then cooling the article so formed.

2. In a method of making porous iron articles the steps of coating iron powder with lead in the desired proportions, molding the coated iron powder to the desired shape in the loose noncompacted condition and then sintering the molded iron powder under suitable non-oxidizing conditions at a temperature sufllcient to melt the of lead wherein ,each particle of iron is coated substantially completely with lead in the form of a thin film thereover, said article being made by sintering together loose non-compacted metal powder. I A

6. A filter element comprising, a highly porous metallic mass made by sintering togetherloos'enon-compacted metal powder wherein the entire porous surface of the element comprises lead and wherein the greater part of the element comprises iron.

7. A ferrous filter element comprising, a highly porous mass of metallic constituent made by sintering together loose non-compacted metal powder," said element having the entire porous surface thereof coated with lead which is present in the entire element in quantities of up 'to 40 percent the remainder of the element being substantially completely iron.

8. A; highly porous filter element comprising iron powder bonded together by means of a substantially nonlcorrodible'insoluble lower melting point metal and wherein each particle of iron is substantially completely coated with said metal, 

